diff --git a/tools/lemon/lempar.c b/tools/lemon/lempar.c
index f945261255..df77e52d4e 100644
--- a/tools/lemon/lempar.c
+++ b/tools/lemon/lempar.c
@@ -640,7 +640,7 @@ static void yy_reduce(
 %%
 /********** End reduce actions ************************************************/
   };
-  assert( yyruleno>=0 && yyruleno<sizeof(yyRuleInfo)/sizeof(yyRuleInfo[0]) );
+  assert( yyruleno>=0 && yyruleno<(int)(sizeof(yyRuleInfo)/sizeof(yyRuleInfo[0])) );
   yygoto = yyRuleInfo[yyruleno].lhs;
   yysize = yyRuleInfo[yyruleno].nrhs;
   yypParser->yyidx -= yysize;